The present invention relates to the recording, storage, and reading of information utilizing high density, multilayer, magneto-optical (HDMMO) media, particularly rotatable MO storage media, such as in the form of thin film disks, and a protective overcoat/lubricant topcoat layer system for contact with cooperating transducer and/or sensor heads or devices.
In recent years, much research and development of MO recording media for use as high density/high capacity memory devices has been carried out. Such media typically comprise a suitable substrate, e.g., of glass, polymer, metal, or ceramic material, coated with a perpendicularly magnetizable film used as a recording medium, typically composed of a rare earth/transition metal thermomagnetic (RE-TM) material, e.g., TbFe, TbFeCo, TbDyFeCo, etc. Information is recorded within the medium by switching the direction of magnetization of desired portions (i.e., domains) of the perpendicularly magnetizable film. More specifically, for recording information, the recording medium is first initialized by applying to the medium a magnetic field from an externally positioned magnetic field generation device (i.e., external magnetic bias), thereby making the direction of the perpendicular magnetization uniformly upwardly or downwardly facing. A first laser beam of sufficiently high power or intensity from a suitable source, e.g., a laser diode, is then irradiated on desired recording portions of the recording medium in the presence of an externally applied magnetic bias field. As a consequence of the laser beam irradiation, the temperature of the irradiated portions (domains) of the recording medium rises, and when the temperature reaches or exceeds the Curie point of the vertically magnetizable film or its magnetic compensation point, the coercive force on the recording portion becomes zero or substantially zero. When this state is achieved at the desired recording portions of the medium, and in the presence of the externally biased magnetic field, the direction of the perpendicular magnetization is switched, e.g., from upwardly facing (=digital logic 1 or 0) to downwardly facing (=digital logic 0 or 1, respectively) or vice versa, so as to be aligned with that of the external magnetic field. At the end of a write pulse (i.e., laser pulse), the temperature of the heated recording domain then decreases and eventually returns to room temperature by cessation of the laser beam irradiation thereof. Since the alignment direction of magnetization of the recording media effected by the laser pulse heating to above the Curie temperature is maintained at the lowered temperature, desired information can thus be recorded in the magneto-optical media.
For reading the information stored in the MO media according to the above-described method, the recorded portions of the media are irradiated with a second, linearly polarized laser beam of lower power or intensity than the one used for recording, and light reflected or transmitted from the recorded portions is detected, as by a suitable detector/sensor means. The recorded information is read out by detecting the Kerr rotation angle of the polarization plane of light reflected from the recording layer or the Faraday rotation angle of the polarization plane of light transmitted through the recording layer. More particularly, since the rotation angle of the polarization plane varies depending upon the direction of magnetization of the recorded portions of the media according to the Kerr or Faraday effect, information stored within the media can be read out optically by a differential detector which decodes the polarization-modulated light beam into bits of information.
Conventional MO recording technology typically utilizes a transparent substrate and the polarized, lower intensity laser beam is transmitted through the recording medium layers for reception by the detector/sensor means for measurement of the rotation angle of the transmitted polarized light via the Faraday effect, as explained supra. However, in high density, multilayer, magneto-optical (HDMMO) recording systems, polarized, lower intensity laser beam light is reflected from a multilayer, superlattice-based MO medium for measurement of the amount of rotation of the plane of the polarized laser light via the Kerr effect, again employing a suitable detector/sensor means, wherein the superlattice provides a greater angle of rotation of polarized light of specific wavelengths, e.g., blue light, than that obtainable with conventional RE-TM materials, e.g., TbFeCo. The HDMMO type system is further advantageous in that, inter alia, opaque substrate materials, e.g., polymers, can be utilized, and dual-sided media are readily fabricated.
In addition to the abovementioned advantages, HDMMO-type media can readily utilize such less expensive polymeric substrates with a pre-formatted servo pattern easily formed on the surface thereof by a masking and injection molding process, thereby not requiring electronic servo as in conventional hard disk drive technology. Further in addition, the direct irradiation of the MO layer(s) via the front side of the medium also results in several other advantages vis-à-vis through-the-substrate illumination, e.g., HDMMO-type systems can utilize head sliders flying over the disk surface by forming the optical and magnetic components integral with the slider, whereby the laser beam is irradiated through the slider body and directly focussed on the HDMO read-write layer. However, conventional overcoat layers and materials, e.g., sputtered SiNx films, are brittle and exhibit poor reliability during head loading, i.e., frequent head crashing, when utilized in HDMMO-type systems, as explained in more detail below.
Such HDMMO-type recording media, when fabricated in disk form for rotation about a central axis, can be adapted for use in conventional Winchester, or hard drive, devices as are employed with conventional magnetic recording media. Hard drives typically employed for such disk-shaped media utilize flying heads for mounting transducer/sensor devices, etc., thereon, for close positioning thereof adjacent the surface of the recording media. In operation, a typical contact start/stop (CSS) method commences when a data transducing head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined small distance from the surface of the disk, where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Therefore, as in the case of magnetic disks, a protective overcoat layer and a lubricant topcoat layer are typically applied to the disk surface for minimizing scratching and abrasion of the sensor/transducer head and the recording media surface, which can result in an undesirably high wear rate of the head and recording media surface.
However, in the case of portable MO recording devices, the use of a lubricating oil, e.g., a fluorocarbon-based oil, is problematic in that it is difficult to maintain the lubricating oil on the surface of the MO media, thereby increasing surface scratching and wear. In addition, MO disks produced without lubricating oil on their surface by some manufacturers are not necessarily compatible with similar media produced with lubricating oil by other manufacturers.
In another approach for minimizing abrasion, scratching, and wear of transducer heads, a solid lubricant is applied to the bottom surface of the flying head which comes into contact with the surface of the MO recording medium. However, such solid lubricant applied to the bottom surface of the flying head must have a durability many times greater than lubricant applied to the MO recording medium. As a consequence, application of solid lubricant only to the flying head is not sufficient for adequately reducing abrasion, scratching, and wear.
An additional difficulty encountered in the development of wear-resistant, lubricated HDMMO-type recording media and Winchester-type drives therefor, is the requirement imposed by the impetus for achieving ever-higher density recording, which necessitates further reduction in the disk-transducer/sensor spacing. The head-to-disk interface (HDI) becomes very critical as head-disk spacing is reduced and head fly height decreases. HDMMO-type media with conventional protective overcoat and lubricant layers, such as sputtered SiNx layers, have extremely poor tribological performance, resulting in lack of reliability of MO-based disk drives.
The above-described problems, including disk crashing during head loading, associated with the requirement for reduced head-disk spacing and fly height, are further exacerbated in the case of HDMMO-type media, wherein the optical and magnetic components of the recording system are incorporated into the head slider.
Thus, there exists a need for a protective overcoat or protective overcoat/lubricant topcoat layer system which enables the manufacture of reliable, high recording density single- and dual-sided HDMMO-type disk devices, which layer system effectively eliminates the problems and drawbacks associated with the conventional technology, i.e., scratching, abrasion, brittleness, increased wear of transducer/sensor head and recording media surfaces, and tendency for crashing during head loading.
The present invention addresses and solves the problems attendant upon the use of high density, HDMMO-type disk-shaped recording media and hard drives, while maintaining full compatibility with all mechanical aspects of conventional disk drive technology.
An advantage of the present invention is a high density, HDMMO-type recording medium having improved tribological performance and long-term durability.
Another advantage of the present invention is a high density, HDMMO-type recording medium having an improved protective overcoat layer.
A further advantage of the present invention is a high density, HDMMO-type recording medium having an improved protective overcoat/lubricant topcoat layer system.
Yet another advantage of the present invention is a high density, HDMMO-type recording medium providing improved performance at decreased head-to-disk spacings.
Still another advantage of the present invention is single- and dual-sided, high density, HDMMO-type recording medium having protective overcoat layer/lubricant topcoat layer systems thereon providing improved tribological performance.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the present invention. The advantages of the present invention may be realized and obtained as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by a high density, multilayer, magneto-optical (HDMMO) storage medium including at least one laminate of layers comprising, in sequence from at least one surface of a substrate: a high density, magneto-optical (HDMO) read-write layer comprising a metal superlattice; a dielectric layer which is substantially transparent to the wavelength(s) of at least one laser beam used for writing and reading out information stored in the medium; and an ultra-thin, amorphous, abrasion-resistant, carbon-based protective flash layer overcoat (FLO) over the substantially transparent dielectric layer.
According to embodiments of the present invention, the amorphous, abrasion-resistant, FLO layer has a thickness not greater than about 10 xc3x85 thick, e.g., from about 5 to about 10 xc3x85, and comprises a diamond-like material selected from a-CNx, a-CHx, and a-CNxHy; the laminate further comprises a lubricant topcoat layer on the protective overcoat layer, the lubricant topcoat layer comprising a fluoropolyether or a perfluoropolyether lubricant material and having a thickness of from about 15 to about 25 xc3x85.
According to further embodiments of the present invention, the substrate includes a pair of opposed major surfaces and comprises a material selected from the group consisting of: polymers, metals, glass, and ceramics; the laminate of layers comprises a stack of layers formed on one of the pair of opposed major surfaces, the layer stack comprising, in overlying sequence from the substrate:
(a) a precious metal or metal alloy layer formed on one of the pair of opposed major surfaces of the substrate;
(b) an HDMO read-write layer comprising a (Co/M)n superlattice, where Co=cobalt, M=a precious metal, and n=about 10 to about 30, the HDMO read-write layer having large perpendicular anisotropy and high coercivity, high squareness ratio (S) for a magnetic hysteresis (M-H) loop measured in the perpendicular direction, and high Kerr rotation angle for red, blue, etc. light;
(c) a dielectric layer comprising a material which is substantially transparent to the at least one laser beam wavelength; and
the FLO layer is formed on the substantially transparent dielectric layer and the lubricant topcoat layer is formed over the FLO layer.
According to embodiments of the present invention:
the precious metal or metal alloy layer (a) comprises an about 100 xc3x85 to about 300 xc3x85 thick layer of a metal material selected from the group consisting of platinum (Pt), palladium (Pd), and alloys thereof;
the HDMO read-write layer (b) comprises a (Co/Pt)n, or a (Co/Pd)n superlattice wherein the thickness of each of the Co layers is from about 3 xc3x85 to about 5 xc3x85, the thickness of each of the Pt and Pd layers is from about 7 xc3x85 to about 10 xc3x85, the perpendicular anisotropy exceeds about 2xc3x97106 erg/cm3, the coercivity is as high as about 5,000 Oe, the squareness ratio of the M-H loop measured in the perpendicular direction is from about 0.85 to about 1.0, and the carrier-to-noise ratio (CNR) is from about 30 to about 60 dB; and
the substantially transparent dielectric layer (c) comprises an about 200 xc3x85 to about 1000 xc3x85 thick layer of a material selected from the group consisting of: SiNx, AlNx, SiOx, and AlOx.
In a further embodiment according to the present invention, the medium comprises another layer stack, identical to the above-described layer stack, formed on the other one of the pair of opposed major surfaces of the substrate.
According to another aspect of the present invention, a high density, multilayer, magneto-optical (HDMMO) storage medium includes at least one laminate of layers comprising, in sequence from at least one surface of a substrate: a precious metal or metal alloy layer; an HDMO read-write layer comprising a metal superlattice; a dielectric layer which is substantially transparent to the wavelength(s) of at least one laser beam used for writing and reading-out information stored in the medium; an ultra-thin, amorphous, abrasion-resistant, carbon-based, protective flash layer overcoat (FLO) over the substantially transparent dielectric layer, the FLO layer having a thickness not greater than about 10 xc3x85 and comprising a diamond-like material selected from the group consisting of: a-CN, a-CHx, and a-CNxHy; and a thin lubricant topcoat layer having a thickness of from about 15 to about 25 xc3x85 on the FLO layer, the lubricant topcoat layer comprising a fluoropolyether polymer material or a perfluoropolyether polymer material.
According to yet another aspect of the present invention, a high density, multilayer, magneto-optical (HDMMO) storage medium includes:
a substrate; and
means for protecting the exterior surface of the medium.
Additional advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein only preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as limitative.